1. Field of the Invention
This invention relates generally to an improved process for melt spinning uniform polymeric filaments into fully oriented yarn, and specifically, to a method and apparatus for spinning polymeric filaments into yarn at high spinning speeds while producing a yarn of high quality.
2. Description of the Background Art
The process of making yarn by melt spinning uniform polymetric filaments through capillaries in a spinneret is well known. Molten polymetric filaments are extruded and withdrawn by a mechanical force from a take-up reel and/or with a high velocity airstream. The finished yarn is wound on a bobbin. The yarn is also treated during the process with an anti-static lubricant called a finish.
U.S. Pat. No. 5,141,700 describes a conventional melt spinning process and device that utilizes positive mechanical drawing with a concurrent flow of gas to assist the withdrawal of the filaments.
Heightened yarn spinning speeds achievable today may run from 7,000 to 10,000 meters per minute velocity of the yarn. The yarn velocity has controlling limits. The first limit is the commercial mechanical speed available from the take-up reel and bobbin. The second speed limit depends on the interaction between properties of material being produced and processing conditions being used in that higher filament speed can be achieved if the drawing force closer to the spinneret surface can be exerted on the filaments where the temperature of the filaments are still high and hence the elongational viscosity is low which allows the filaments to be readily drawn at higher rate without forcing the filaments to break.
The production of partially oriented yarns allows filament spinning speeds up to 3,000 to 4,000 mpm according to the formula of V(f) equals Q.div.d.times.9,000 where V(f) is filament velocity, Q is throughput grams per hole per minute and d is the filament denier as d is designed for end products. Q is proportioned to V(f). The higher the filament velocity we can reach, the higher production and throughput. The reason for filament speeds of 4,000 mpm reached in partial oriented yarn production limits is probably that the filament or the melt exiting from the orifice of the spinneret is cooled down much too soon and too fast, therefore causing the elongation viscosity of the polymer melt to increase too quickly and too high resulting in high spin line tension. If one were to increase the take-up speed or the draw down force more, it would simply force the filaments to break.